Operando Measurements of Electrolyte Li-ion Concentration during fast charging with FTIR/ATR

Abstract

The ability to charge a Li-ion battery at high charging rates is critical for electric vehicle adoption; however, further study of ion transport is required to develop electrolytes suitable for fast charge. Fourier transform infrared spectroscopy (FTIR) used with attenuated total reflection (ATR) enables operando measurements of liquid electrolytes. This research focused on solvation shifting of solvent infrared absorption bands in the presence of lithium ions. Lithium-shifted infrared absorption bands and non-shifted bands of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) were compared to infer ion concentration changes during cycling. Lithium concentrations were calibrated using EC/EMC/LiPF6 electrolytes with known lithium concentrations. A Li-ion half-cell with a graphite anode and EC/EMC/LiPF6 electrolyte was observed with FTIR/ATR. The results showed that the magnitude of lithium concentration changes increased with increasing C-rate. During a galvanostatic intermittent titration technique (GITT) test, changes in lithium concentration could be observed. During intercalation, a lithium depletion occurred when a negative current was applied, and a lithium surplus occurred during deintercalation when a positive current was applied. The capability of observing lithium concentration has significant implications for the utility of operando studies and the potential to link lithium movement to battery performance.

Synchrotron radiation based operando characterization of battery materials

“…Infrared spectra can thus constitute a ngerprint for some of the components of electrolytes, the SEI and organic electrode materials. Operando measurements would therefore enable the investigation of not only the evolution of the cation solvation structure in the electrolyte 117,118 but also the redox mechanisms and/or degradation processes for organic electrodes. 119 Unfortunately, the study of the formation of the SEI and related passivation layers is limited by the fact that they are commonly very thin (between 5 and a few tens of nm) and consist of compounds containing functional groups similar to those present in the electrolyte they originate from, which is present inside the cell.…”

Decoding the puzzle: recent breakthroughs in understanding degradation mechanisms of Li-ion batteries

“…A recent study focused on solvation shifting of solvent infrared absorption bands in the presence of lithium ions, comparing lithium-shifted and non-shifted bands of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) to infer changes in ion concentration during cycling. 140 Lithium concentrations were calibrated using EC/EMC/LiPF 6 electrolytes with known concentrations. A Li-ion half-cell with a graphite anode and EC/ EMC/LiPF 6 electrolyte was examined using FTIR/ATR.…”

Fast‐Charging Strategies for Lithium‐Ion Batteries: Advances and Perspectives

“…Understanding the solvation structure and interfacial transport kinetics of electrolyte is another key step to realize fast-charging of LIBs. Santhanagopalan et al [91] found that Fourier transform infrared spectroscopy (FTIR) combined with attenuated total reflection (ATR) enables operational measurements of liquid electrolyte. At higher charging rates, an increase in local Li + consumption and accumulation due to insufficient ion transport is observed.…”